1. Field of the Invention
The invention relates to an improved fuel injection system employing a pressure booster for use in an internal combustion engine.
2. Description of the Prior Art
For better comprehension of the specification and claims, several terms will now be defined: The fuel injection system of the invention can be embodied as either stroke-controlled or pressure-controlled. Within the context of the invention, the term stroke-controlled fuel injection system is understood to mean that the opening and closing of the injection opening is effected with the aid of a displaceable nozzle needle, on the basis of the hydraulic cooperation of the fuel pressure in a nozzle chamber and in a control chamber. A pressure reduction inside the control chamber causes a stroke of the nozzle needle. Alternatively, the deflection of the nozzle needle can be effected by a final control element (actuator). In a pressure-controlled fuel injection system of the invention, the nozzle needle is moved counter to the action of a closing force (spring) by the fuel pressure prevailing in the nozzle chamber of an injector, so that the injection opening is uncovered for an injection of the fuel from the nozzle chamber into the cylinder. The pressure at which fuel emerges from the nozzle chamber into a cylinder of an internal combustion engine is called injection pressure, while the term system pressure means the pressure at which fuel is available or kept on hand inside the fuel injection system. The term fuel metering means furnishing a defined fuel quantity for injection. The term leak fuel, or leakage is understood to mean a quantity of fuel that occurs in operation of the fuel injection system (such as a guide leakage) and that is not used for injection and is pumped back to the fuel tank. The pressure level of this leak fuel can have a standing pressure, and after that the fuel is depressurized to the pressure level of the fuel tank.
Many engine manufacturers want to have a shallow pressure increase edge at the onset of the injection. Often, a boot phase is also wanted, for reducing emissions. In fuel injection systems with pressure chambers of the kind known for instance from German Patent Disclosure DE-A1 199 10 970, the pressure chamber can be used for shaping the course of injection. Thus the desired course of injection can be realized without additional parts such as deflection pistons. To vary the pressure course, the motion of the piston of the pressure chamber can be utilized. Varying the inlet cross section to the high-pressure-side pressure booster chamber as a function of stroke is known from U.S. Pat. No. 5,568,317. hereby incorporated by reference. This US patent proposes a multi-stage control of the inlet cross section.